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  • Dynamic Dispatch without Virtual Functions

    - by Kristopher Johnson
    I've got some legacy code that, instead of virtual functions, uses a kind field to do dynamic dispatch. It looks something like this: // Base struct shared by all subtypes // Plain-old data; can't use virtual functions struct POD { int kind; int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); }; enum Kind { Kind_Derived1, Kind_Derived2, Kind_Derived3 }; struct Derived1: POD { Derived1(): kind(Kind_Derived1) {} int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); // plus other type-specific data and function members }; struct Derived2: POD { Derived2(): kind(Kind_Derived2) {} int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); // plus other type-specific data and function members }; struct Derived3: POD { Derived3(): kind(Kind_Derived3) {} int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); // plus other type-specific data and function members }; and then the POD class's function members are implemented like this: int POD::GetFoo() { // Call kind-specific function switch (kind) { case Kind_Derived1: { Derived1 *pDerived1 = static_cast<Derived1*>(this); return pDerived1->GetFoo(); } case Kind_Derived2: { Derived2 *pDerived2 = static_cast<Derived2*>(this); return pDerived2->GetFoo(); } case Kind_Derived3: { Derived3 *pDerived3 = static_cast<Derived3*>(this); return pDerived3->GetFoo(); } default: throw UnknownKindException(kind, "GetFoo"); } } POD::GetBar(), POD::GetBaz(), POD::GetXyzzy(), and other members are implemented similarly. This example is simplified. The actual code has about a dozen different subtypes of POD, and a couple dozen methods. New subtypes of POD and new methods are added pretty frequently, and so every time we do that, we have to update all these switch statements. The typical way to handle this would be to declare the function members virtual in the POD class, but we can't do that because the objects reside in shared memory. There is a lot of code that depends on these structs being plain-old-data, so even if I could figure out some way to have virtual functions in shared-memory objects, I wouldn't want to do that. So, I'm looking for suggestions as to the best way to clean this up so that all the knowledge of how to call the subtype methods is centralized in one place, rather than scattered among a couple dozen switch statements in a couple dozen functions. What occurs to me is that I can create some sort of adapter class that wraps a POD and uses templates to minimize the redundancy. But before I start down that path, I'd like to know how others have dealt with this.

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  • XMLEncoder in java for serialization

    - by tom
    Im just wondering how i use xmlencoder to serialize ArrayList where foo is my own made class. Do i have to do anything in particular, ie define my own xml structure first and then call toString on each value in my list and write it out? Can anyone point me to a good tutorial? http://java.sun.com/products/jfc/tsc/articles/persistence4/ Thats what i have been looking at but it doesnt seem to mention what to do with non library classes. Thanks

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  • How to link a property setter to a delegate?

    - by Danvil
    I would like to give a property setter to a delegate. How is this done? class A { private int count; public int Count { get { return count; } set { count = value; } } } A a = new A(); delegate void ChangeCountDelegate(int x); ChangeCountDelegate dlg = ... ? // should call a.Count = x

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  • jQuery treat hover on two elements as one elements

    - by davewilly
    I have an image map which I have overlaid with some markers in the form of anchors. I currently have a hover trigger on each image map area and the associated anchor - as shown in screen shot I need to treat these two elements as one, as currently when mouse is moved out of one onto the other it calls .hover() and callback again. I want to call hover callback only when mouse is moved out of either elements.

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  • try .. catch blocks - when to use

    - by Konrad
    I have always been of the belief that if a method can throw an exception then it is reckless not to protect this call with a meaningful try block. I just posted 'You should ALWAYS wrap calls that can throw in try, catch blocks.' to this question and was told that it was 'remarkably bad advice' - I'd like to understand why. Thanks!

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  • undefined method `parameterize' for nil:NilClass

    - by Senthil
    I've been trying to do SEO friendly urls, and managed to get it work, but when I call index action on blogs, I get a weird "undefined method `parameterize' for nil:NilClass." The method works when using show method. def to_s title end def to_param "#{id}-#{to_s.parameterize}" end

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  • Android Assets - Unable to access

    - by BahaiResearch.com
    Using this code it should return a list of the assets. But it crashes, with a "Source not found, Edit Source Lookup Path..." message in the debugger when I call the list method: @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); AssetManager assets = this.getAssets(); try { //error happens on this next line String[] l = assets.list(null); } catch (IOException e) { } }

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  • Different behavior of reflected generic delegates with and without debugger

    - by Andrew_B
    Hello. We have encountered some strange things while calling reflected generic delegates. In some cases with attatched debuger we can make impossible call, while without debugger we cannot catch any exception and application fastfails. Here is the code: using System; using System.Windows.Forms; using System.Reflection; namespace GenericDelegate { public partial class Form1 : Form { public Form1() { InitializeComponent(); } private delegate Class2 Delegate1(); private void button1_Click(object sender, EventArgs e) { MethodInfo mi = typeof (Class1<>).GetMethod("GetClass", BindingFlags.NonPublic | BindingFlags.Static); if (mi != null) { Delegate1 del = (Delegate1) Delegate.CreateDelegate(typeof (Delegate1), mi); MessageBox.Show("1"); try { del(); } catch (Exception) { MessageBox.Show("No, I can`t catch it"); } MessageBox.Show("2"); mi.Invoke(null, new object[] {});//It's Ok, we'll get exception here MessageBox.Show("3"); } } class Class2 { } class Class1<T> : Class2 { internal static Class2 GetClass() { Type type = typeof(T); MessageBox.Show("Type name " + type.FullName +" Type: " + type + " Assembly " + type.Assembly); return new Class1<T>(); } } } } There are two problems: Behavior differs with debugger and without You cannot catch this error without debugger by clr tricks. It's just not the clr exception. There are memory acces vialation, reading zero pointer inside of internal code. Use case: You develop something like plugins system for your app. You read external assembly, find suitable method in some type, and execute it. And we just forgot about that we need to check up is the type generic or not. Under VS (and .net from 2.0 to 4.0) everything works fine. Called function does not uses static context of generic type and type parameters. But without VS application fails with no sound. We even cannot identify call stack attaching debuger. Tested with .net 4.0 The question is why VS catches but runtime do not?

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  • Using jQuery to perform a GET request and using the resulting data

    - by Filip Ekberg
    I have a page, let's call it "callme.html" which only has this content: abc Now I want to fire the following: $.get("callme.html", function (data) { alert(data); }, "text"); I am using jQuery 1.4.2 mini and the page is called but the alert is empty. Any ideas why? I'd like the popup to contain abc I've also tried the following $.ajax({ url: "callme.html", async: false, success: function (data) { alert(data); } });

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  • Best Practice: Direct SQL Access vs. Web Service

    - by phsr
    With respect to an application that has both a web and desktop client version: What is the best practice for the desktop client which needs access to a SQL Server? What are the benefits of connecting to the database from the application vs using a web service? Which one provides better security? What type of scope would call for one vs the other (enterprise intranet vs. web app, etc) Are there any other considerations that are necessary when choosing on platform?

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  • Create lags with a for-loop in R

    - by cptn
    I've got a data.frame with stock data of several companies (here it's only two). I want 10 additional columns in my stock data.frame df with lagged dates (from -5 days to +5 days) for both companies in my event data.frame. I'm using a for loop which is probably not the best solution, but it works partially. DATE <- c("01.01.2000","02.01.2000","03.01.2000","06.01.2000","07.01.2000","09.01.2000","10.01.2000","01.01.2000","02.01.2000","04.01.2000","06.01.2000","07.01.2000","09.01.2000","10.01.2000") RET <- c(-2.0,1.1,3,1.4,-0.2, 0.6, 0.1, -0.21, -1.2, 0.9, 0.3, -0.1,0.3,-0.12) COMP <- c("A","A","A","A","A","A","A","B","B","B","B","B","B","B") df <- data.frame(DATE, RET, COMP, stringsAsFactors=F) df # DATE RET COMP # 1 01.01.2000 -2.00 A # 2 02.01.2000 1.10 A # 3 03.01.2000 3.00 A # 4 06.01.2000 1.40 A # 5 07.01.2000 -0.20 A # 6 09.01.2000 0.60 A # 7 10.01.2000 0.10 A # 8 01.01.2000 -0.21 B # 9 02.01.2000 -1.20 B # 10 04.01.2000 0.90 B # 11 06.01.2000 0.30 B # 12 07.01.2000 -0.10 B # 13 09.01.2000 0.30 B # 14 10.01.2000 -0.12 B this loop works fine comp <- as.vector(unique(df$COMP)) mylist <- vector('list', length(comp)) # create lags in DATE for(i in 1:length(comp)) { print(i) comp_i <- comp[i] df_k <- df[df$COMP %in% comp_i, ] # all trading days of one firm df_k <- transform(df_k, DATEm1 = c(NA, head(DATE, -1)), DATEm2 = c(NA, NA, head(DATE, -2)), DATEm3 = c(NA, NA, NA, head(DATE, -3)), DATEm4 = c(NA, NA, NA, NA,head(DATE, -4)), DATEm5 = c(NA, NA, NA, NA, NA, head(DATE, -5)), DATEp1 = c(DATE[-1], NA)) #DATEp2 = c(DATE[-2], NA, NA), #DATEp3 = c(DATE[-3], NA, NA, NA), #DATEp4 = c(DATE[-4], NA, NA, NA, NA), #DATEp5 = c(DATE[-5], NA, NA, NA, NA, NA)) mylist[[i]] = df_k } df1 <- do.call(rbind, mylist) But if I add the lines with DATEp2, DATEp3, DATEp4, DATEp5. the code doesn't work. Can anybody tell me what I'm doing wrong here? Here the code with all the lagged dates. # create lags in DATE for(i in 1:length(comp)) { print(i) comp_i <- comp[i] df_k <- df[df$COMP %in% comp_i, ] # all trading days of one firm df_k <- transform(df_k, DATEm1 = c(NA, head(DATE, -1)), DATEm2 = c(NA, NA, head(DATE, -2)), DATEm3 = c(NA, NA, NA, head(DATE, -3)), DATEm4 = c(NA, NA, NA, NA,head(DATE, -4)), DATEm5 = c(NA, NA, NA, NA, NA, head(DATE, -5)), DATEp1 = c(DATE[-1], NA), DATEp2 = c(DATE[-2], NA, NA), DATEp3 = c(DATE[-3], NA, NA, NA), DATEp4 = c(DATE[-4], NA, NA, NA, NA), DATEp5 = c(DATE[-5], NA, NA, NA, NA, NA)) mylist[[i]] = df_k } df1 <- do.call(rbind, mylist)

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  • What technology should i choose for this kind of an application?

    - by Pandiya Chendur
    One of my client has asked me an application Telephone answering machine which is exactly like customer care voice application (ie) he is maintaining a college, parents of students will call to a college phone no and they will be asked to enter student roll/reg no and they can hear that student attendence percentage,mark etc.... Is it possible? If so, How can i pass a student detail to that voice recorded.... I dont what kind of technology can be used to make this application possible...

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  • How do I specify a relative local file path in DOS?

    - by donde
    I am using c#.NET 2.0 to execute DOS commands to ftp a file. All works except for 1 thing, in the cmd file I call, it runs a PUT statement. Right now the put statement has a hardcoded local file path. I need to specify a dynamic path. I've tried put %~dp0\myfile.DTL myfile.dtl but it says it can't find the file.

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  • Accessing PCI Device from user space programs

    - by crissangel
    I have a device which would be interface with my processor through pcie. I have written driver for it using the existing pci file operations. Now my problem is how do I access it from user space programs? PCI File operations do not have IOCTL support and hence I cant make an ioctl call unlike other char devices. I cannot use pci_config_read_byte etc. functions as they are meant for kernel space(included in linux/pci.h).

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  • How can I set a traget to top for a link within an iframe?

    - by digitup
    in my code for index.html I use jQuery and have a link with id #button3. I have used in index.html $('#button3 a').attr({ target: '_top' }); When I call the index.html from an iframe as a src, the page opens in _self. I have tried with _blank and still when clicking on the a link it doesn't open on a new page. Any tips?

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  • Do something before closing the browser window

    - by Adam Kiss
    Hello, we have an web-application built in flash (it's actually just getting built :D) where is very important to be notified, when user closes his window. Since it's in flash, we do not worry about Javascript, we do not support non-javascript users. What is the safest (meaning it's 100% sure it gets called) X-browser way to call php script to close session, make some db changes, etc.? Thank you

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  • WPF Binding to IDictionary<int,MyType>.Values Doesn't Respond to Property Changes?

    - by Phil Sandler
    I am binding a ListView a property that essentially wraps the Values collection (ICollection) on a generic dictionary. When the values in the dictionary change, I call OnNotifyPropertyChanged(property). I don't see the updates on the screen, with no binding errors. When I change the property getter to return the Linq extension dictionary.Values.ToList(), without changing the signature of the property (ICollection) it works with no problem. Any reason why the Values collection bind and notify properly without projecting to an IList<?

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  • Clean Javascript Info Popup

    - by steve
    I'm just trying to figure out exactly what kind of script this is, and where I can find more info on implementing it. Not sure exactly what to call it. If you click on one of the speakers here, you can see it in action: http://www.howconference.com/speakers/

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  • A single button should be used in all the forms.

    - by mugamath
    i need to use a single button for all forms in a vb.net project. The single button should be called in the forms to perform operations. For eg., In a form i need to save, update the records. When i call the button, save and update buttons should be appeared at runtime using the single button. guide me....

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  • Request a Windows Phone 7.5 Location

    - by Christopher Cabezudo Rodriguez
    I am trying to track 5 windows phone 7.5 for a experiment and I have try using an app (that I am developing for that experiment) but the app must be active and that's not possible for all readings, I was looking online and I find something similar that Microsoft has done with the find my phone service, https://www.windowsphone.com/en-US/find Anyone knows how can i call that service outside the website or any other way to accomplish this task i need GEO position every 15 min

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  • how to write or create (when no exist) a file using python and Google AppEngine

    - by zjm1126
    this is my code: f = open('text/a.log', 'wb') f.write('hahaha') f.close() and it is not create a new file when not exist how to do this , thanks updated class MyThread(threading.Thread): def run(self): f = open('a.log', 'w') f.write('hahaha') f.close() error is : Traceback (most recent call last): File "D:\Python25\lib\threading.py", line 486, in __bootstrap_inner self.run() File "D:\zjm_code\helloworld\views.py", line 15, in run f = open('a.log', 'w') File "d:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 1188, in __init__ raise IOError('invalid mode: %s' % mode) IOError: invalid mode: w

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